Automated stationary/portable test system for photoconductive drums

ABSTRACT

An automated test system is provided for evaluating characteristics of photoreceptors used in the electrophotographic process. The test system includes a retainer for holding the photoreceptor, typically in the form of a cylinder or drum, high voltage power supplies, a charging device, light sources, and non-contact electrostatic surface potential probes, the entirety of the test system enclosed in a light-proof cabinet. A control unit responsive to user defined parameters automatically performs tests for drum substrate surface cleanliness, photoreceptor layer thickness, physical defects, and electrophotographic properties. Linear and circular scanning and fixed adaptable systems are shown.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/040,770, filedMar. 31, 1993, which is a continuation of application Ser. No.07/975,380, filed Nov. 12, 1992, (now abandoned).

FIELD OF THE INVENTION

The invention relates to methods for nondestructive evaluation ofmaterials and more particularly to tests for photoreceptors.

BACKGROUND OF THE INVENTION

A key component in many copy machines and laser printers is aphotoreceptor onto which a powdered "ink" or toner is deposited in aprecise pattern. The pattern is generated by light exposure, andcorresponds to the images or letters to be copied or printed. Paper isplaced into contact with the photoreceptor, toner is transferred to thepaper, and the "inked" paper is subjected to heat and pressure to fusethe toner onto the paper. The photoreceptor is then wiped clean of anyremaining toner, and the process is repeated.

Among many possible configurations, an important commercialphotoreceptor design is a multilayer structure wherein a metal drum iscoated with an insulating polymer base layer, and an organicphotoconductive (OPC) overcoat consisting of a charge generating layerand a charge transport layer. In the copying or laser printing process,deposition of the toner on the photoconductive drum is effected bycreating a negatively or positively charged pattern on the drum to whichoppositely charged particles of toner powder cling. This initial chargedpattern is created by imparting a charge of the desired polarity to theentire drum. After electrostatic charging, the cylinder is carefullyexposed to a pattern of light which causes charge carriers to be freedwithin the charge generating layer of the drum. These charge carriers,under the influence of the existing electric field, migrate through thecharge transport layer, neutralize the deposited charge, therebyelectrically discharging those portions. The remaining charged portionsof the surface correspond to the pattern to which the toner iselectrostatically attracted.

To produce clear and consistent images, the photoconductive drum must beable to consistently accept a sufficient level of charge, hold thecharge for a sustained period of time in the dark, and discharge rapidlyunder controlled light exposure over repeated cycles. Devices presentlyexist which enable tests of certain charge build-up, charge retention,and discharge characteristics to be performed. However, these devicesare not suitable for measuring other quality characteristics during themanufacture of new drums, or in the recycling of used drums. Thesecharacteristics include the cleanliness of the underlying metal drumsurface, the uniformity of thickness of the polymer base and chargegeneration layers, the presence of layer defects, and various measuresof electrophotographic performance across the entire drum surface.

While generalized techniques for nondestructive detection andcharacterization of flaws in materials, such as those described in U.S.Pat. No. 4,443,764 to Suh et al. are known, there is no automated testapparatus or series of tests that is capable of evaluating the fullrange of photoconductive drum characteristics that bear on printquality. Such tests and an easily operated apparatus for performing themwould be important to quality control during manufacture andrefurbishment of products having photoconductive drums.

SUMMARY OF THE INVENTION

The present invention provides a fully automated test system capable ofperforming a comprehensive series of tests to evaluate the numerouscharacteristics of the various layers of a photoreceptor, such as aphotoconductive drum, which affect its print performance. The testsinclude complete electrophotographic characteristic evaluation, defectmapping, layer thickness measurement and uncoated drum substratecleanliness testing.

The user can select and test for the cleanliness of the uncoated drumsurface; the thickness of the drum's base coating polymer (with orwithout a charge generating layer thereon) and of the charge generatinglayer itself; the presence of defects in the base, charge generating,transport layers; as well as the charge build-up, charge retention anddischarge characteristics of the completed drums.

A further feature of the invention is a test system including a controlunit responsive to user defined parameters for controlling preprogrammedtests; a test station including a drum retainer for holding and rotatingthe drum, a charging system having a high voltage power supply and apolarity selector, a light source for causing localized electrostaticdischarge, a broad spectrum light source for causing globalelectrostatic discharge, and a low voltage and a high voltagenon-contact electrostatic surface potential probe; a light-proof cabinetfor enclosing the test station; an adjustable fixture for the chargingsystem, high voltage and low voltage probes and electronics therefor fordrum scanning, a mounting ring to provide convenient positioning andadjustment of the probes and light source; and motors to produce drumrotation and ring movement; and an output device for presenting testresults to a system operator.

The drum substrate surface cleanliness test includes completely scanningthe drum by the low voltage electrostatic sensor to measure contactpotential values or the surface potential on the surface of the drum todetect surface contamination.

The layer thickness test can be run on a drum having a base polymerlayer with or without the charge generating layer thereon. Byappropriate use of charge polarity and discharge light, the thickness ofeach layer is determined from the differences in charge mobility andphotosensitivity of the two layers.

The defect test is typically run on a fully layered drum. The drum ischarged during a scan and the resulting potential on the drum surface isimmediately measured. In this test, different combinations of testconditions including the light exposure level and charge polarityprovide indications of different types of defects.

The electrophotographic measurement test is conducted on a fully layereddrum. The system continuously monitors the potential on the drum surfaceat a predefined set of locations while sequentially performing each ofthe following operations for a predefined time duration: imparting anelectrostatic charge to the drum; allowing the charge to decay in thedark; and finally illuminating at least a portion of the drum surfacewith light of a preselected wavelength and intensity to causeelectrostatic discharge. Parameters which characterize theelectrophotographic performance of the drum are obtained and/or computedfrom the acquired data. The entire test sequence is repeated many timesto perform a cyclic fatigue test of the drum.

A further feature of the invention is a test system including a chargingdevice, a voltage measurement probe, and a light source that areconveyed linearly along a photoconductive drum for performing voltageacceptance and discharge testing.

Yet another feature of the invention is a life-cycle test for comparingvoltages imparted to a drum and residual voltages after discharge by alight source to life-cycle reference voltages for a similar drum.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the invention can may be better understoodwith reference to the accompanying specification and the drawings inwhich:

FIG. 1A is a schematic of a test system used to evaluate aphotoreceptor;

FIG. 1B is a perspective view of instrumentation used in the test systemof FIG. 1A;

FIG. 2 is a flow-chart of user selected computer controlled testsperformed by test system of FIG. 1, that are coordinated and analyzed bya control unit;

FIG. 3 is a depiction of a parameter selection display for the substratecleanliness test of FIG. 2, provided by the user interface of thecontrol software for the control unit of FIG. 1;

FIG. 4 is a graphical representation of the results of the substratecleanliness test of FIG. 2;

FIG. 5 is a depiction of a parameter selection display for the layerthickness measurement test of FIG. 2, provided by the user interface ofthe control software for the control unit of FIG. 1;

FIG. 6 is a graphical representation of the results of the layerthickness measurement test of FIG. 2;

FIG. 7 is a depiction of a parameter selection display for the defectmapping test of FIG. 2, provided by the user interface of the controlsoftware for the control unit of FIG. 1;

FIG. 8 is a graphical representation of the results of the defectingmapping test of FIG. 2;

FIG. 9 is a depiction of a parameter selection display for theelectrophotographic performance test of FIG. 2, provided by the userinterface of the control software for the control unit of FIG. 1;

FIG. 10 is a graphical representation of the results of theelectrophotographic performance test of FIG. 2;

FIG. 11 is a top view of an alternative instrumentation configurationfor the test system of FIG. 1A;

FIG. 12 is a perspective view of another embodiment of the test systemof FIG. 1A;

FIG. 13 is a graphical representation of life cycle testing resultsperformed with the test system of the invention;

FIG. 14A is a graphical representation of defect mapping test resultsfor a photoreceptor after a first usage cycle;

FIG. 14B is a graphical representation of defect mapping test resultsfor a photoreceptor after a second usage cycle;

FIG. 14C is a graphical representation of defect mapping test results ofa photoreceptor after a second usage cycle;

FIG. 15A is a graphical representation of a charging defect map; and

FIG. 15B is a graphical representation of a discharge defect map.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is a schematic of a test system used to perform nondestructiveinspection and testing of thin dielectric coatings of photoreceptorsused in electrophotography, such as an organic photoconductive drum 10having a metallic core coated with a polymer base layer, a chargegenerating layer, and a charge transport layer.

The test system includes a test station 12 located within a light-proofcabinet 14, a control unit 16, and one or more input/output devices 18.

The test system is uniquely able to integrate several test functions forthe photoreceptor, a charge generating layer, a base layer, and anuncoated drum in a single, fully-computerized system. These testfunctions evaluate the quality characteristics that are most critical tothe performance, re-usability and longevity of the drum 10. Although thefocus of the ensuing description is directed toward photoconductivedrums, substantially the same process and equipment can be used forother photoreceptor geometries, such as belts and flat plates.

Evaluations performed by the test system include: 1) surface cleanlinessof an uncoated drum substrate; 2) thickness and uniformity of a thinpolymer base layer and a charge generation layer; 3) physical defects ona new or recycled drum 10; and 4) electrophotographic performance of anew or recycled drum 10. Each of the tests can be performed overrepeated cycles without conducting any or all of the other tests.

In an exemplary embodiment of the hardware components depicted in FIG.1A, the test station 12 has a drum retainer comprising tapered upper andlower spindles, 20 and 22 respectively, that are adapted to position thedrum 10 for testing and electrically ground the metallic substrate ofthe drum 10. The lower spindle 22 is in a fixed position with respect tothe test station and is insertable into either of the hollow ends ofdrum 10. The lower spindle is equipped with a cone 23 partially platedwith a noble metal, such as gold, that serves as a reference electrode,and a mushroom shaped positioning aid 25 that supports the drum 10 innear axial alignment with the upper spindle 20. The upper spindle 20 isslidably retained on a track 24 and is also insertable into either ofthe hollow ends of the drum 10. The upper spindle 20 is also equippedwith a positioning cone 21 for axial alignment of the drum 10. Prior toconducting tests, a first end of the drum 10 is placed onto the lowerspindle 22, after which the upper spindle 20 is lowered into engagementwith the opposite end of the drum 10. When the drum 10 has end-caps,such as those used for remanufacture of cartridges, the upper and lowerpositioning cones, 23 and 21 respectively, are replaced with fittingsadapted to correctly position the drum 10 and to provide an electricalground connection to the metallic substrate of the drum 10. In anotherembodiment, fixed-location adapters are used to position and retainphotoreceptors of different sizes and types in lieu of the movable upperspindle 20. In each of the embodiments, an automatic, motorized systemis optionally incorporated for positioning the upper spindle 20 orfitting to hold and release the upper end of the drum 10.

Typically, the test station 12 is configured to accommodate a drum 10 upto 400 mm long and having an 80 mm outer diameter (O.D.), however, otherdrum sizes can also be accommodated. The entire test station is housedin the light-proof cabinet 14 which measures approximately 18"×24"×34"in one embodiment. It should be noted that although the test station 12and drum 10 are depicted in a vertical orientation, other orientationssuch as horizontal are equally functional and compatible with theconcept of the invention. various instrumentation to perform and monitortests are placed within cabinet 14 including: a charging device 26, suchas a scorotron, a corotron, or a roller charger energized from positiveor negative high voltage power sources 28, the polarity of which isselected by a polarity selection switch 30 which is software controlled.A low voltage, non-contact, electrostatic surface potential probe 32, ora high voltage, non-contact, electrostatic surface potential probe 34;and a first light source 36 for discharging a localized portion of thedrum 10 are positioned on a carrier ring 40 to face the drum 10 as it isrotated. A second light source 38 for global discharge of the drum 10 ispositioned on a wall of the light-proof cabinet. The high voltage probe34 performs measurement in the KV range, or alternatively the lowvoltage probe 32 can be used to measure charge in the mV to V range.Normally, the low voltage probe 32 is used for the cleanliness test andthe high voltage probe 34 is used for all of the other tests. Thecarrier ring 40 and the instrument mounting can be adapted to easilyretract from the drum 10 to facilitate loading and unloading of the drum10 and to preclude interference with end-caps on a drum so equipped.

While the first light source 36 which causes localized discharge of thedrum 10 can be selected from a variety of known light sources, such as alaser diode, a multi-wavelength (red-green-blue) LED is especiallyuseful for providing a quick assessment of the drum's sensitivity. Theselection of wavelength is related to the wavelength used to dischargethe drum 10 in specific applications. In an alternative configuration,selection of wavelength is accomplished by providing a bandpass colorfilter through which light from a broad spectrum source, such as atungsten or halogen lamp, is projected. Neutral density filters areprovided for adjusting light intensity and a shuttering mechanismprovides a means for controlling exposure time. The second light source38 used for discharging the entire drum 10 is a high-performancefluorescent lamp or an array of light emitting diodes.

Referring to FIG. 1B, the charging device 26, one or more voltage probes32,34, and one or more broad spectrum light sources 36 are mounted oncircular carrier 40 via adapters or holders 42.

A first stepper motor 44 is coupled to the lower spindle 22 and enablesthe drum 10 mounted thereon to be variably rotated over a range of 0.1to 5 revolutions per second with an angular resolution for drum rotationof 0.225°. A second stepper motor 46 is coupled to the carrier 40 toenable the carrier and the instrumentation thereon to be moved axiallyon the track 24. The axial scan speed is variable over a range ofapproximately 0.25 to 127 mm per second (0.01 to 5 inch per second) andthe axial scan range is approximately 50 cm (20"), with a minimum stepsize of 0.0381 mm (0.0015"). As a result, the instrumentation carrier 40can scan past all of the useable surface of the drum. It should be notedthat most of the drum motion parameters can be modified and extended ifnecessary. As a safety feature, an electromechanical interlock 48 isprovided on the light-proof cabinet 14 to prevent the high voltage powersupply 28 from energizing when the cabinet door 50 is opened.

FIG. 1B is a perspective view of a portion of the test station 12wherein the carrier 40 is located at an intermediate location on thetrack 24 and illustrates an embodiment of instrument positioning on thecarrier 40. In this view, the first light source 36, the charging device26, and the electrostatic probes 32, 34 are shown in proximity to, butnot in contact with the drum 10.

All motion and scan operations of the test station are controlled by thecontrol unit 16, typically a microcomputer which interfaces with theinstrumentation including: light source drivers 52, motor drivers 60 and62, and a high voltage source driver 64. The control unit 16 interfaceswith the system operator via one or more output/input devices 18 such asa video monitor, printer, a keyboard and the like.

Software used by the control unit 16 to run the comprehensive series oftests may be written for a graphical user interface such as MicrosoftWindows (registered trademark of Microsoft Corporation). The softwareallows any of the built-in tests to be performed at will using a widerange of test parameters. The software is also readily expandable topermit customized testing. For each of the software controlled tests,data is sampled from one of the probes at a fixed rate throughout thescanning procedure. After the data have been acquired, key parametersare calculated. It should be noted that the characteristics discussedhereinbelow are merely exemplary and the software may easily be alteredto suit user requirements. FIG. 2 is a flow-chart of user selected testsperformed by the test system of FIG. 1A using the software, and shouldbe referred to in conjunction with the description of the various testsassociated with FIGS. 3-10.

Each of the tests are fully computer-controlled and can be performed forboth research and development and manufacturing quality controlpurposes. For research and development testing, the charge and dischargecharacteristics of the photoreceptor provide a direct measure of thefunctional performance of a specific coating formulation. For qualitycontrol evaluation, the system operator can select predefined tolerancelimits to determine the acceptability of a finished product or arecycled drum.

From a main menu state the system operator specifies the photoreceptortype to be tested in step 63, followed by selecting the tests to beperformed in step 65 which may include any or all of tests for:substrate surface cleanliness 66; layer thickness 80; physical defect90; or electrophotographic performance 100.

Selecting the test for substrate surface cleanliness 66 tests thephotoreceptor for the presence of surface contaminants that wouldinterfere with the adhesion or operation of the base layer and thephotoconductive layer applied to the conductive metal, typicallyaluminum, drum.

The cleanliness test begins, as do all of the tests, by having thesystem operator define the test parameters through the FIG. 3 interfacein a step 68. For the cleanliness test, which may be performed on theuncoated metal drum or any conducting surface, these parameters includean initial sample situs, a final sample situs, an intermediate samplespacing increment, a sampling speed, and the option of charging on/offand charging polarity.

FIG. 3 is a depiction of a parameter selection display for an exemplarysubstrate cleanliness test 66, wherein the exemplary initial axialposition of the low voltage probe 32 mounted on the carrier 40 is userset to 0.500 inches from a reference point, such as an end of the drum10. The final axial position is user set to 10.500 inches from thereference point. The carrier 40 is user commanded to move along thetrack 24 by the second step motor 46 in increments of 0.039 inches perdrum revolution, and the drum 10 is user set to be rotated by the firstmotor 44 at a speed of 2.00 revolutions per second. Sample measurementsare user specified to be taken in 0.037 inch increments. The chargingdevice 26 is not activated. After making any corrections to theparameters, the system operator accepts the parameters in a step 70 byclicking on "OK" and initiates the cleanliness test in a step 72,causing in turn the measurement and calculating steps 74 and 76 to berun.

When the cleanliness test 66 is initiated, the carrier 40 and drum 10begin their programmed movements. The low voltage electrostatic probe 32is scanned over the surface of the drum 10 and the voltages detected arerepresentative of contact potential values in step 74 and these are usedto calculate the degree and location of detrimental contaminants such asfingerprints or other organic/inorganic films, with the test resultspresented in step 78 on an output device 18 or stored for futurereference, such as lifetime tracking of individual photoreceptors. FIG.4 is an exemplary screen display, which may be gray scale but isnormally colored to improve discrimination of regions on the cleanlinessmap for the entire drum surface. At the completion of the cleanlinesstest the system returns to the menu state 65 so that another test can beperformed.

The test system is also used to perform a layer thickness test entailingstep 80, wherein an individual coating layer thickness and uniformity,such as the base layer and or the charge generation layer are evaluated.This test begins by user defining of test parameters in step 68, throughthe user interface of FIG. 5 and includes an initial sample situs, afinal sample situs, an intermediate sample spacing increment, a samplingspeed, an electrostatic charge level, and an electrostatic chargepolarity. Additional parameters defined for the layer thickness test instep 68 include the layer to be tested, discharge light wavelength(s),and light intensity for purposes described below.

In FIG. 5 the initial axial position of the carrier 40 is 0.500 inchesfrom a reference point. The final axial position is 10.500 inches fromthe reference point. The carrier 40 is commanded to move along the track24 in increments of 0.039 inches per drum revolution, and the drum 10will be rotated at a speed of 2.00 revolutions per second. Samplemeasurements will be taken in 0.037 inch increments. The charging device26 is set at a 6.000 kV charging voltage.

When the system operator accepts the parameters in a step 70 andinitiates the layer thickness test of steps 82-88, the drum 10 ischarged. The charging device 26, such as a corotron, charges a smallportion of the drum, which is then optionally illuminated, and then theprobe measures the residual voltage. This process is continuous whilethe drum rotates and the carrier 40 moves so that the entire drumsurface is passed over by the charging device 26 as indicated in step82. The drum surface is optionally illuminated in step 84, and thecarrier 40 and drum 10 make their programmed movements while the probetakes measurements of the residual charge over the defined whole orportion of the drum 10 at the preselected increments. Quantitativevalues of thickness are estimated and based on a predeterminedcalibration curve, and a distribution map of layer thickness iscalculated in step 88 and output in step 78 in a desired form for thesystem operator.

The layer thickness test 80 can be run on a drum 10 with the basepolymer with or without the charge generating layer by appropriateselection of charging device polarity and light discharge.

To measure the thickness of a base layer without another layer thereon,either a positive or a negative charge can be applied in step 82 to thedrum 10 by the charging device 26. Scanning the surface of the drum 10to measure, in step 86, the residual charge held by the layer after apassage of time, allows its thickness to be calculated as previouslydescribed in step 88.

To test the thickness of the base layer and charge generating layer whenboth have been applied onto the drum 10, a positive charge is used.Because the charge generating layer will hold a positive charge, thethickness of the base and charge generation layers can be calculated instep 88 by evaluating its charge decay without illumination in step 84.

The thickness of the base and charge generating layers are separatablydeterminable by using a negative charge, and running step 84 todischarge the charge generation layers leaving the base layer charged.The thickness calculated for the base layer is subtracted from thecombined layer thickness to determine the thickness of the chargegenerating layer.

FIG. 6 is an exemplary screen display of layer thickness map of theentire drum 10. At the completion of the layer thickness measurement,the system returns to the main menu in state 65 so that another test ofthe drum 10 can be performed.

In another test, the test system detects localized physical defects suchas pin-holes or scratches, or distributed defects such as wear marks,non-uniform coating thickness, or poor dispersion of the light-sensitivedye, on the drum surface which can affect the quality of a print inelectrophotography. The physical defect test begins by having the systemoperator enter the test in step 90 from state 65. Many of the same testparameters as the layer thickness test are defined in step 68, byreference to FIG. 7, namely an initial sample situs, a final samplesitus, an intermediate sample spacing increment, a sampling speed, anelectrostatic charge level, an electrostatic charge polarity, anddischarge light wavelengths and intensities.

FIG. 7 depicts a parameter selection display for an exemplary defectmapping test, wherein the initial axial position of the high voltageprobe 34 is 0.500 inches from a reference point. The final axialposition is 10.500 inches from the reference point. The carrier 40 iscommanded to move along the track 24 in increments of 0.039 inches perdrum revolution, and the drum 10 will be rotated at a speed of 2.00revolutions per second. Sample measurements will be taken in 0.037 inchincrements. The charging device 26 is set at a 5.000 kV chargingvoltage. After making any corrections to the parameters, the systemoperator accepts them in step 70, and initiates the test in step 72.

When the defect mapping test is initiated, the charging device 26imparts in step 92 the selected charge to the drum surface, optionallyin step 94 followed by illuminating at least a portion of the drumsurface with the selected light source 36 to see how well the drum 10holds a charge or discharges. The carrier 40 and drum 10 begin theirprogrammed movements directly after charge up while the probe 34 takesmeasurements over the defined surface in step 96 of the held or residualcharge on the drum 10 at the preselected increments. By detecting chargeirregularities over a known time interval as the drum 10 rotates andinstruments move, the location and size of defects are calculated 98,and a defect map can be created and output 78 to the system operator.

For the embodiment illustrated, the spatial resolution of the defectmapping test is approximately 0.010 inch. FIG. 8 is an exemplary screendisplay of a defect map of the entire drum 10, which indicates alocalized defect. At the completion of the defect mapping test thesystem returns to the main menu state 65 so that another test can beperformed.

The test system can also be used to test electrophotographic performanceon a fully layered new or recycled drum 10. The electrophotographicmeasurement test comprises several critical functional tests on the drum10 including charge acceptance, dark decay rate, light decay rate,residual voltage, spectral sensitivity, and cyclic fatigue. This testbegins by selection from the menu in step 100 and defining in step 68test parameters including an initial sample situs, a final sample situs,a number of intermediate sample locations, a rotational speed, anelectrostatic charge level, an electrostatic charge polarity, anddischarge light wavelength(s) and intensities. The parameters alsoinclude time intervals for charge, dark decay, light decay, and numberof cycles and cycles between samples.

FIG. 9 is a depiction of a parameter selection user interface displayfor an exemplary electrophotographic measurement test, whereinmeasurements are taken by the high voltage probe 34 at 2.500 inches froma reference point, at 5.500 inches, and at 8.500 inches from thereference point. The drum 10 will be rotated at a speed of 5.00revolutions per second. The charging device 26 is set at a 5.000 kVcharging voltage for 10 seconds to the drum 10 followed by a dark decayof 5 seconds and a light decay of 10 seconds. The test will typicallycycle plural times through the sequence of steps 102-112 for eachreport. Red light at maximum intensity (100%) will be used to dischargethe drum 10. After making any corrections to the parameters, the systemoperator accepts the test parameters in step 70, and initiates the test100 in step 72.

FIG. 10 is a graphical representation of results of one location for atypical electrophotographic measurement test, in this case a location2.500 inches down the drum. When the test is initiated at "t_(i) " time,an initial (pre-charging) voltage measurement "V_(i) " 102 is made.

The charging device 26 then imparts the selected charge in step 104 tothe drum 10 for the predetermined time interval of 10 seconds, duringwhich time the drum surface potential is continuously measured andrecorded. At time "t_(a) ", marking the conclusion of the charging step104, the drum surface potential which indicates the level of chargeacceptance is donated as "V_(a) " 106. The charged drum 10 is then leftin the completely light-proof cabinet 14 for the selected dark decaytime interval of 5 seconds, while the surface potential is continuouslymeasured and recorded. At time "t_(o) ", marking the conclusion of thedark decay step 108, the drum surface potential is denoted as "V_(o) ",the drum 10 is then illuminated in step 110 with the selected light andsource 38 for the selected light decay interval of 10 seconds, while thesurface potential is continuously measured and recorded. Various keyparameters are determined in step 112: the time elapsed for theilluminated area to discharge fifty percent is denoted as "t₅₀ "; theresidual surface potential is denoted "V_(r) " and is defined as thesurface potential at time "t_(r) " which is at five times t₅₀ relativeto t_(o). Finally, the time at the completion of light discharge isdenoted as "t_(f) " and the surface potential at that time is denoted as"V_(f) ". Other key parameters can be defined and calculated, such as"R_(dd) ", the percentage of acceptance voltage retained during darkdecay, defined as V_(o) divided by V_(a). The entire test sequence canbe repeated at the same location for any desired number of times and/orat other drum locations.

In addition to the scanning techniques described above that employ asingle probe to measure contact or surface potential of thephotoreceptor, it is also possible to use two probes simultaneously toaccelerate data collection and to further enhance the accuracy of thetests.

Referring to FIG. 11, a two probe configuration for the test station 12is shown in a top view. In this configuration, a charge measurementprobe 35 and a discharge measurement probe 37 are mounted on the carrier40 with the first light source 36 interposed between them. As the drum10 rotates in the direction indicated by the arrow, a region of the drumis charged by the charging device 26. Next, the charge held by the drumin that region is measured by the probe 35, following which a region ofthe drum is discharged by the first light source 36. Immediatelythereafter, the effectiveness of the discharge in the target region ismeasured by the discharge measurement probe 37. The above describedsequence enables a 360° scan of the drum 10 to be performed in fractionsof a second, after which the carrier 40 is commanded to displace apredetermined increment along the axis of the drum 10, wherein thescanning sequence is continued. The above described helical scan enableselectrophotographic measurements to be taken over the entire surface ofthe drum or selected regions very rapidly for processing to evaluate thephotoreceptor.

FIG. 12 illustrates yet another configuration of the test station 12,wherein an instrumentation cluster 120 including at least onemeasurement probe 122, a discharge light source 126, and a chargingdevice 126 moves linearly on a track 128 aligned parallel with and inclose proximity to a photoconductive drum 10. The track 128 is movableto allow adjustment for accommodating drums of different diameters. Thedrum 10 has end-caps 130 by which a mandrel 140 retains the drum 10 inposition for testing. The mandrel 140 is coupled to a motor 142 thatrotates the drum 10 either continuously or incrementally in an indexedmanner. A reversible polarity power supply 144 energizes theinstrumentation cluster 120, which along with the power supply 144 andindexing motor 142 are responsive to a control unit 146, such as amicroprocessor or computer. The control unit is responsive to operatorinput from input devices known in the art and presents control optionsand test results on output devices known in the art, these devicesreferred to collectively as I/O devices 148.

The measurement principals used by the test station illustrated in FIG.12 are the same as those described hereinabove with respect to the teststation of FIG. 1A. However, the tests are performed in a slightlydifferent manner due to the configuration of the instrumentation cluster120. For example, as the instrumentation cluster 120 moves from block Atoward block B, the charging device 126 imparts a charge to the drum 10which is immediately evaluated by the measurement probe 122. The drum 10is then held stationary while the instrumentation cluster 120 returns toa starting point proximate block A from which a subsequent scan towardblock B is recommenced. In the subsequent scan, the discharge lightsource 124 is activated to discharge the drum 10, the discharge of whichis immediately evaluated by the measurement probe 122. In anotherembodiment, the charging device 126 is adjacent a charge measurementprobe, adjacent to a light source, adjacent to a discharge measurementprobe, allowing a complete test to be performed in a single linear scan.

Although the drum 10 can be rotated and scanned until the drum 10 hasbeen evaluated through 360° of rotation, tests have revealed thatbecause degradation is largely the same around the drum at each axialdisplacement evaluation of a single linear scan is often sufficient tomake an accurate useability determination for the drum 10. Therefore,because the drum does not need to be rotated, the motor 142 can beeliminated without adversely affecting test results. Elimination of themotor combined with a concomitantly simplified retaining structure forthe drum and the compact configuration of the instrumentation cluster120, results in a test station markedly smaller, lighter, and lessexpensive than prior art devices which are unable to perform the batteryof tests performed by the present invention. Accordingly, the entiretest station illustrated in FIG. 12, is transportable to a user or othersite by a maintenance technician.

If full drum testing is desired, the drum is rotated a fixed angle (e.g.10-30°) after the linear scan, and a new scan generated.

The test system of the invention permits life cycle testing ofphotoconductors which degrade over time. FIG. 13 is a graphicaldepiction of the dark decay voltage versus the charge acceptance voltagefor six photoconductors of the same type over three cycles of use at theindicated test voltages. For convenience, one cycle is defined as usingthe same photoconductor to print 3,000 standard sheets of paper. Anotherway to track cycles is one cycle per toner cartridge for a typical laserprinter. As can be determined from the graph, the photoreceptors degradein a fairly consistent manner from cycle to cycle. This enables a testsystem operator to test a photoreceptor having an unknown or unmonitoreduse state and compare it to the test results for a similar typephotoreceptor to determine its cycle age and life remaining. For aphotoreceptor at a known cycle, the test results indicate whether thephotoconductor is ageing properly. Thus, the system software enables anoperator to compare test results of a tracked photoreceptor with itsstored life history or to compare test results of an untrackedphotoreceptor with a stored calibration curve for that type ofphotoreceptor. The operator can also input the level of performancedegradation acceptable to a particular photoreceptor application or userwhich is compared to the drum being tested to establish a simplepass-fail test output.

Referring now to FIGS. 14A, 14B, and 14C, graphical illustrations areshown corresponding to a first cycle (new drum), a second cycle(slightly used drum), and a third cycle (more heavily used drum),respectively. As with the graphs of FIGS. 4, 6 and 8, the graphicaloutput can be gray scale or colored to represent voltages or defects atvarious points or regions on the photoreceptor. It should be noted thatthe voltage values for a 360° scan of a drum are generally consistent ata given axial position. Thus, although a full 360° scan provides a veryaccurate representation of an entire drum, an axial scan taken at anygiven angular position provides adequate data for life cycle predictionsto be made, as described with respect to the test station illustrated inFIG. 12.

The flexibility of the software also allow an operator to select fordisplay only user defined significant voltage values, such as thoseindicated on the charging defect map of FIG. 15A and on the dischargedefect map of FIG. 15B.

Although the invention has been shown and described with respect toexemplary embodiments thereof, various other changes, omissions andadditions in form and detail thereof may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A test for conducting an evaluation ofelectrophotographic performance of a photoconductive drum including thesteps of:defining test parameters including electrostatic charge level,electrostatic charge polarity, a charge interval, a dark decay interval,a light decay interval, a number of test cycles, a light wavelength anda light intensity for at least one light source, an initial samplesitus, a final sample situs, intermediate sample spacing increment, andsampling speed; accepting said test parameters; initiating said test;measuring an initial charge level at a predetermined number of locationson said photoconductive drum as programmed during said step of definingtest parameters; imparting an electrostatic charge to saidphotoconductive drum with said charging device; measuring a chargepotential retained by said photoconductive drum at said predeterminednumber of locations; allowing a period of time to elapse; measuring saidcharge potential retained after said period of time has elapsed;illuminating at least a portion of said photoconductive drum with saidat least one light source to cause electrostatic discharge; measuring atime interval for said electrostatic charge potential to decay to apredetermined percentage of its original level; measuring a residualelectrostatic charge potential at said predetermined number of locationsat a predetermined time interval; and calculating and displayingelectrophotographical performance and key measurement parameter at saidlocation as a compilation of data acquired during said test.
 2. The testof claim 1, wherein said photoconductive drum comprises a layeredphotoreceptor having a substrate covered by a polymeric base layer,covered by a charge generation layer, with or without a charge transportlayer.
 3. The test of claim 1 wherein said electrophotographicalperformance measurement is dark decay rate and said display is agraphical representation ot said dark decay rate at said locations. 4.The test of claim 1 wherein said electrophotographical performance ameasurement is charge acceptance and said display is a graphicalrepresentation of said charge acceptance at said locations.
 5. The testof claim 1 wherein said electrophotographical performance measurement isspectral sensitivity and said display is a graphical representation ofsaid spectral sensitivity at said locations.
 6. The test of claim 1wherein said electrophotographical performance measurement is residualvoltage and said display is a graphical representation of said residualvoltage at said locations.
 7. The test of claim 1 wherein saidelectrophotographical performance measurement is cyclic fatigue and saiddisplay is a graphical representation of said cyclic fatigue at saidlocations.